1. Field of Invention
This invention relates to devices used to control the temperature of water delivered to a domestic shower or bath user, specifically to devices that allow the user to preset the temperature of such delivered water, and to devices that automatically maintain a supply of water at the desired temperature despite changes in water pressure, so reducing the probability of scalding caused by sudden temperature change. Specifically this invention relates to such devices that may be easily retrofitted to existing plumbing systems without the disassembly of piping and without the use of specialized plumbing tools.
2. Description of the Prior Art
Domestic water delivery systems typically comprise pipes for the delivery of both hot and cold water. Conventionally, the temperature of water delivered to a bath, shower and the like is adjusted through the manual operation of valves. In such systems it is common for the temperature of delivered water to fluctuate suddenly by as much as about 20.degree. C. so producing an uncomfortable temperature change and, more seriously, a serious possibility of scalding. Conventional manual valve controls have no way of mitigating these effects.
The most common prior art method for adjusting temperature of delivered water is by sensing the water temperature by hand and then manually turning the faucets as desired.
Automatic means for regulating water temperature have also been disclosed, and the prior art includes the use of a solenoid-operated water valve, connected to hot and cold water pipes, controlled by a series of relay switches wired in series. These relays are controlled by a logic circuit which receives input from a flow-rate sensitive, or temperature sensitive switch (U.S. Pat. No. 5,125,433). In this prior art patent the simple logic circuitry comprises a pulse shaper circuit, a reset pulse circuit and a gate pulse circuit.
It is also known to use a vibrator switch to compare a control signal, produced by a preset control output (chosen by pushing a button), with the signal derived from a temperature sensor positioned somewhere at the water outlet, and to process this differential signal by means of a differential amplifier and a limiter which is then used to activate a reversible motor, opening or closing a water valve, thereby adjusting the flow of water (U.S. Pat. No. 4,421,269). Both the above prior art references allow for push-button selection of shower water temperature.
Another prior art reference describes an electrically operated shut-off valve which closes in response to a preset temperature sensed by a temperature sensor, thereby order to shut off the flow of water during freezing conditions (U.S. Pat. No. 5,240,028).
Another references describes the use of a shut-off valve actuated via a temperature sensitive electric one-way solenoid (U.S. Pat. No. 5,090,436).
Another prior art patent uses a thermostatic valve at the shower head which senses when the delivered water is "too hot" and automatically shuts off the flow of water, in this invention, to restart the water flow, the valve must be manually reset (U.S. Pat. No. 4,281,790).
Another prior art device teaches a temperature sensitive water diverting means which at a preset (uncomfortably hot or cold) temperature diverts the water away from the user and instead directs the water against the shower wall, when the water temperature becomes comfortable again, the water flow reverts back to the shower user (U.S. Pat. No. 4,854,499).
Prior art inventions that simply shut off the flow of water to the user or diverts the flow of water away from the user do not adequately address the desired aim of delivering a constant flow of water to a user at a steady, unvarying temperature.
The prior art also does not solve the problems of rapid temperature fluctuations of delivered water because the response time of the prior art inventions contains an inherent and significant lag allowing very hot water to reach the user for a significant time before the the temperature is corrected (see FIGS. 1 and 2). Such rapid temperature fluctuations occur when cold water pressure suddenly drops, such as when a toilet is flushed.
Systems that use relay or mechanical inventions, and systems employing proportional-only control circuitry, simply cannot respond to sudden temperature changes fast enough to avoid scalding.
Systems that employ derivative circuitry (such as the invention as described in U.S. Pat. No. 4,421,269, which employs a differential amplifier, a limiter circuit, a polarity relay and a vibrator switch to compare current signals), may provide an improvement over proportional-only circuitry, but these still possesses a significant inherent lag before correcting the water temperature.
Prior art inventions such as those described in U.S. Pat. No. 5,125,433 and U.S. Pat. No. 4,241,269 do not teach the use of an internal low voltage DC dry cell power supply but instead seem to use an external AC mains supply which is rectified and transformed. The presence of an electrical connection between a high voltage AC mains supply and the shower water delivery system poses obvious safety hazards. These hazards are addressed and eliminated in the present invention by the use of internal dry cells. Also, the present invention facilitates easy installation by an untrained member of the public by avoiding the requirement for connecting the device to any AC mains power supply.
Further, the prior art also does not solve the need for a device that controls and corrects for sudden water temperature changes that may be easily and relatively cheaply retrofitted to an existing water delivery system, such as a shower, without the disassembly of piping and without the use of specialized plumbing tools.
There is a need for a device that responds rapidly to sudden water temperature changes in the water delivery pipes and is able to adjust the flow of water through the delivery valve so rapidly that the temperature of the water delivered to a user is relatively constant, and comfortable and cannot result in scalding.
There is a need for such a device that can also be easily and relatively cheaply retrofitted to an existing water delivery system, such as a shower, without the disassembly of piping and without the use of specialized plumbing tools.
The present invention solves the problem of speed of response and temperature adjustment by using a microprocessor. Particularly the present invention can use a dual gain control system which maximizes the speed of temperature mitigation. The present invention can use a microprocessor to calculate both derivative gain and proportional gain, so producing a rapid and accurate output signal that controls the action of the mixer valve in response to both actual discrete, quantum temperature changes and to the rate of such temperature changes. Fuzzy logic circuitry can be used in the present invention to make such calculations and to increase the rate of response.
The present invention also allows a number of users to preset temperatures for their own comfort, such preset temperatures being stored in the memory of the device, whether in a microprocessor or by some other electric or mechanical means, and to select this preset temperature before entering the shower, so negating the need for manual "trial and error" adjustment.
The present invention is also designed so that any layman, with no plumbing experience and the minimum of mechanical ability may retrofit the device to an existing water delivery system. The unit is completely self-contained and possesses its own internal power supply. Fitting can be done in minutes with the use of a screwdriver and an adjustable wrench.